The present invention relates to a base film for a transparent conductive thin film suitable for use in a transparent touch panel or the like. In particular, it relates to an easy adhesion film which, when formed thereon with a transparent conductive thin film such as an indium-tin oxide film to obtain a transparent conductive film sheet, improves the durability of the transparent conductive thin film, particularly the adhesiveness of the transparent conductive thin film thereof. Still more particularly, it relates to such an easy adhesion film suitable for use in a touch panel of a color liquid crystal display.
The liquid crystal display has recently drawn attention as an image display device and is expected to be used increasingly in portable electronic notebooks, information terminals and the like. As an input device for portable electronic notebooks and information terminals, a transparent touch panel overlaid on the liquid crystal display device is commonly used. The resistance film type touch panel is a frequent choice for its low cost.
The generally used resistance film type touch panel has a structure in which a transparent conductive film sheet and a glass provided with a transparent conductive thin film are disposed across a proper gap. As the transparent conductive film sheet, a transparent polymer film provided with a transparent conductive thin film such as indium-tin oxide (ITO) is generally used.
As the transparent polymer film of the transparent conductive film sheet, there is used a film having a surface in which many fine protrusions and recesses with specific ranges of a maximum height and an arithmetical mean deviation are formed by embossing in order to prevent the Newton ring which occurs when the touch panel is touched (pressed) (Japanese Patent Application Un-examined Publication No.H8-77871 (""96).
In the transparent conductive film sheet using the above-mentioned transparent polymer film, however, adhesion of the transparent polymer film to the transparent conductive thin film is insufficient. A problem of poor durability therefore arises when the transparent conductive film sheet is used in a touch panel. Specifically, the transparent conductive thin film is likely to peel off or be abraded. Up to now, a film having high durability when provided with a transparent conductive thin film and also having anti-Newton ring property has not been available.
On the other hand, owing to advances in the color performance of CRTs and flat panel displays using touch panel displays and also higher color definition in various displays, a problem has arisen that, when a conventional transparent conductive film sheet subjected to a surface roughening treatment for preventing occurrence of the Newton ring is used in a touch panel, the high-definition color screen, particularly the white portions thereof, produce glare.
Accordingly, an object of the present invention is to provide an easy adhesion film for a transparent conductive thin film, that is excellent in durability when the transparent conductive thin film is provided thereon and capable of preventing occurrence of the Newton ring when it is used in a transparent conductive film sheet of a touch panel of a conventional liquid crystal display. Another object of the present invention is to provide an easy adhesion film for a conductive thin film, that is capable of preventing glare of a color screen when it is used in a touch panel of a color liquid crystal display and is suitable for use in touch panels of both monochrome and color liquid crystal displays.
To attain the above objects, the inventors conducted extensive studies on the relationship between the rough surface of a transparent conductive film sheet used in a touch panel of a color liquid crystal display, namely, the surface thereof formed with a transparent conductive thin film, and the glare of the color screen. As a result, it was found that, since protrusions and recesses of the conventional base film are regular and smooth, the surface functions as lenses, enlarges and emphasizes the RGB light-emitting points, which are the source of the color display, and consequently the color screen produces glare. They accomplished the present invention based on this knowledge.
Specifically, the easy adhesion film for a transparent conductive thin film of the present invention is obtained by imparting an easy adhesion property to a transparent polymer film used as a base film on which the transparent conductive thin film is to be formed. The easy adhesion film is also made capable of preventing occurrence of the Newton ring without producing a lens effect by using two kinds of matting agents having different particle diameters to control the shape of the surface.
An easy adhesion film for a transparent conductive thin film according to a first aspect of the present invention comprises a transparent polymer film and an easy adhesion layer formed on the transparent polymer film, which easy adhesion layer is composed of at least an ionizing radiation curable resin, a thermoplastic resin binder and two or more kinds of matting agents having different average diameters.
In the easy adhesion film for a transparent conductive thin film according to the first aspect, the matting agents preferably consist of at least two kinds of matting agents having an average diameter of 1-15 xcexcm and an average diameter of 5-50 nm.
An easy adhesion film for a transparent conductive thin film according to the second aspect of the present invention comprises a transparent polymer film, a transparent hard coat layer containing at least an ionizing radiation curable resin and a matting agent having an average diameter of 1-15 xcexcm formed on the transparent polymer film, and an easy adhesion layer for a transparent conductive thin film containing at least an ionizing radiation curable resin, a thermoplastic resin binder and a matting agent having an average diameter of 5-50 xcexcm formed on the transparent hard coat layer.
In the easy adhesion film for a transparent conductive thin film of the second aspect, the thickness of the transparent hard coat layer is preferably 2-15 xcexcm and the thickness of the easy adhesion layer for a transparent conductive thin film is preferably 0.2-1.5 xcexcm.
The present invention also provides a transparent conductive film sheet comprising a base film and a transparent conductive thin film formed on the base film, wherein the base film is one the above-mentioned easy adhesion films according to the present invention.
By use of the easy adhesion film for a transparent conductive thin film of this invention, there can be provided a transparent conductive film sheet excellent in durability when a transparent conductive thin film is formed, by providing an easy adhesion layer comprising at least an ionizing radiation curable resin binder, a thermoplastic resin binder and matting agents, and, as the matting agents of the easy adhesion layer or using a matting, using two kinds of matting agents having different average diameters or using a matting agent having a relatively small diameter and providing a hard coat layer containing a matting agent having a relatively large diameter between the transparent polymer film and the easy adhesion layer. This transparent conductive film sheet can prevent occurrence of the Newton ring when it is used in a touch panel of the conventional liquid crystal display and also prevent glare of a color screen when it is used in a touch panel of a color liquid crystal display. Accordingly, the present invention can provide a transparent conductive film sheet suitable for use in both touch panels of monochrome and color liquid crystal displays.